The report divides consumers into three types in terms of their banking expertise: "savvy," who use direct deposit and avoid fees whenever possible; "basic," who aren't as proficient at avoiding fees and have at least one overdraft fee a month; and "inexperienced," who make heavy use of services but typically pay two overdraft fees a month.

Then, the researchers applied those characteristics to more than 200 checking accounts offered by the 12 largest banks, and 52 prepaid cards available online, to see which accounts best-suited each category.

For savvy consumers, checking accounts are the most economical, with a median monthly cost of about $4, compared with $4.50 for prepaid cards. Inexperienced consumers, however, did better with prepaid cards, which cost them a median of about $29 a month, compared with $94 for checking accounts.

Still, the cards carry myriad fees, and disclosure isn't uniform. So just because a card doesn't disclose that it charges a fee, for instance, doesn't mean that it doesn't charge it. There's simply no way for consumers to know until they end up incurring the charge.

Also, balances on prepaid cards don't always have clear protection from F.D.I.C. insurance, the report found. If a bank fails, the agency reimburses deposits up to $250,000. But many companies that offer prepaid cards aren't banks and don't hold the funds themselves. Rather, they pool funds in large accounts at a third-party bank, where the money may be covered by so-called "pass-through" insurance, which may be more tenuous, the report says.

Of the 52 cards Pew studied, only three indicated that they lacked F.D.I.C. insurance. But there is no federal oversight or supervision of prepaid companies that aren't banks, to make sure the proper requirements for the insurance are met, Pew found.

"Claims of F.D.I.C. insurance in cases where portions of consumers' funds may in fact be uninsured create a false sense of security for unsuspecting consumers," the report said.